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This study investigated the optimum conditions to maximize the inactivation of biofilms using both plasma-treated solutions and post-treatment storage conditions. Chemical properties of plasma-treated solutions were also analyzed to identify their possible biofilm inactivation mechanisms. Escherichia coli O157:H7 biofilms on stainless steel were prepared and immersed in distilled water (DW), 100 ppm of sodium chloride solution (NaCl), or 100 ppm of sodium hypochlorite solution (NaOCl), followed by container-type plasma treatment for 10 min (15 kHz and 250 W). After plasma discharge was switched off, biofilms immersed in the plasma-treated solution were stored for 10 min with the plasma apparatus closed or open. The log reduction of E. coli O157:H7 was NaOCl (3.58) > NaCl (2.06) = DW (1.95) in the closed storage condition. In addition, the bactericidal effect of NaOCl was higher in the closed condition than in the open condition. Concentrations of the hydroxyl radical (OH·) and peroxynitrite (ONOO−) were also the highest for NaOCl in the closed condition. Consequently, plasma treatment using NaOCl solution in the closed condition was found to be the optimum method for inactivation of E. coli O157:H7 biofilms, due to high hydroxyl radical and peroxynitrite concentrations. This method also has the merit of using a lower concentration of NaOCl than that used typically in industry.

Magnetic field configuration is critical in Hall thrusters for achieving high performance, particularly in thrust, specific impulse, efficiency, etc. Ion beam features are also significantly influenced by magnetic field configurations. In two typical magnetic field configurations (i.e., co-current and counter-current configurations) of a cylindrical Hall thruster, ion beam characteristics are compared in relation to multiply charged ions. Our study shows that the co-current configuration brings about high ion current (or low electron current), high ionization rate, and small plume angle that lead to high thruster performance.

We derive analytic formulas describing the temporal behavior of the laser-induced incandescence (LII) signal in both case of the heat transfer governed by radiation and collision. Using these formulas, we can describe the temporal behavior of the LII signal and determine the dimension of nanosize particles in low-pressure plasma. Simple calibration procedure is introduced for quantitative measurement of the particle size with the LII technique.

Multiply charged ions and plume characteristics in Hall thruster plasmas are investigated with regard to magnetic field configuration. Differences in the plume shape and the fraction of ions with different charge states are demonstrated by the counter-current and co-current magnetic field configurations, respectively. The significantly larger number of multiply charged and higher charge state ions including Xe4+ are observed in the co-current configuration than in the counter-current configuration. The large fraction of multiply charged ions and high ion currents in this experiment may be related to the strong electron confinement, which is due to the strong magnetic mirror effect in the co-current magnetic field configuration.

Plasma plume and thruster performance characteristics associated with multiply charged ions in a cylindrical type Hall thruster (CHT) and an annular type Hall thruster are compared under identical conditions such as channel diameter, channel depth, propellant mass flow rate. A high propellant utilization in a CHT is caused by a high ionization rate, which brings about large multiply charged ions. Ion currents and utilizations are much different due to the presence of multiply charged ions. A high multiply charged ion fraction and a high ionization rate in the CHT result in a higher specific impulse, thrust, and discharge current.

Atmospheric pressure plasma (APP) has been recognized as a promising tool for cancer therapy based on its ability to remove cancer cells by causing apoptosis and necrosis. However, the effect of APP on the neighboring tissues of tumors remains unknown. Moreover, the role of APP on the vessels near tumors could be very important, because once a tumor becomes vascularized, the potential for metastasis can increase dramatically. We show in the present study that APP can induce cell cycle arrest in endothelial cells and further suppress the angiogenesis process. These results strongly support the use of APP in cancer treatment.

The electron-atom neutral bremsstrahlung continuum radiation emitted from weakly ionized plasmas is investigated for electron density and temperature diagnostics. The continuum spectrum in 450–1000 nm emitted from the argon atmospheric pressure plasma is found to be in excellent agreement with the neutral bremsstrahlung formula with the electron-atom momentum transfer cross-section given by Popovic. In 280–450 nm, however, a large discrepancy between the measured and the neutral bremsstrahlung emissivities is observed. We find that without accounting for the radiative H2 dissociation continuum, the temperature, and density measurements would be largely wrong, so that it should be taken into account for accurate measurement.

As many as eight multiple plasma bullets produced at atmospheric pressure were observed in one voltage period in a capillary helium dielectric barrier plasma jet. We found that the number of the bullets strongly depends on the nitrogen fraction added to the helium supply gas. Using optical emission spectroscopy and ionization rate calculation, this study demonstrates that nitrogen gas plays an important role in the generation and dynamics of multiple plasma bullets through Penning ionization of nitrogen by helium metastables.

Investigation of the radial scale effect on low-power cylindrical Hall thrusters has been undertaken by comparing the thrusters with three different channel diameters of 28, 40, and 50 mm. The investigation found that both the anode efficiency and the thrust of the larger thruster are higher as the anode power is raised. On the other hand, higher current and propellant utilizations are achieved for the smaller thruster, which is due to higher neutral density and better electron confinement. The large plume angle of the small cylindrical Hall thruster causes thrust loss, resulting in the reduction of anode efficiency.

Spatial distribution, growth, and morphology of the nanoparticle were investigated in the plasmas with relatively low and high ion densities. Our experimental results reveal that cauliflower-shaped amorphous nanoparticles are dominantly distributed throughout the entire plasma in the low ion density plasma while spherical crystalline particles are spread near the plasma edge in the high ion density plasma. Only agglomeration growth step of the nanoparticles was observed without molecular accretion growth step in the high density plasma. Based on the experimental and numerical results, the role of ion density in the growth mechanism and transport of the nanoparticles is discussed.

Performance characteristics of low power cylindrical Hall thrusters are investigated in terms of the length of the discharge channel. Thrust, efficiency, discharge current, and propellant utilization are evaluated for different channel lengths of 19, 22, and 25 mm. It is found that the propellant utilization and ion energy distribution function are strongly associated with the channel length. Increase of thrust and efficiency are also found with increasing channel lengths. These characteristics of the thruster are interpreted with possible generation of multi-charged ions due to increased residing time within the extended space inside the channel.

When treated by atmospheric pressure plasma, human liver cancer cells (SK-HEP-1) and normal cells (THLE-2) exhibited distinctive cellular responses, especially in relation to their adhesion behavior. We discovered the critical threshold voltage of 950 V, biased at the electrode of the micro-plasma jet source, above which SK-HEP-1 started to detach from the substrate while THLE-2 remained intact. Our mechanical and biochemical analyses confirmed the presence of intrinsic differences in the adhesion properties between the cancer and the normal liver cells, which provide a clue to the differential detachment characteristics of cancer and normal cells to the atmospheric pressure plasma.

The temporal behavior of naturally produced dust parameters (radius and density) and plasma parameters (electron temperature and ion flux) was investigated in radio frequency SiH4/H2/Ar plasmas. As a result, the electron temperature and ion flux were shown to be strongly correlated with the three-step dust growth pattern. In addition, the generation of dust particles was suppressed by mixing more hydrogen gas due to the plasma chemistry, and consequently, the dust growth rate in the molecular accretion growth, which is known to be proportional to the growth rate of thin film deposition, increased.

Atmospheric pressure helium plasma treated human hepatocytes exhibit distinctive zones of necrotic and live cells separated by a void. We propose that plasma induced necrosis is attributed to plasma species such as oxygen radicals, charged particles, metastables and/or severe disruption of charged cytoskeletal proteins. Interestingly, uncharged cytoskeletal intermediate filaments are only minimally disturbed by plasma, elucidating the possibility of plasma induced electrostatic effects selectively destroying charged proteins. These bona fide plasma effects, which inflict alterations in specific subcellular structures leading to necrosis and cellular detachment, were not observed by application of helium flow or electric field alone.

Atmospheric pressure helium discharge characteristics were investigated for varying driving radio frequencies in the range between 1.86 and 27.1 MHz. As the driving frequency is raised, both gas breakdown and α-γ transition voltages decrease due to the reduction in the electron drift loss. In addition, different discharge features such as normal, abnormal, α, and γ modes show certain dependences on the frequency. Using a simple circuit model, the changes in sheath thickness from 2.35 to 0.11 mm, electron density from 0.26 to 15.6×1011 cm−3 was obtained by raising the frequency from 1.86 to 27.1 MHz.

Microsize jet-type plasmas were generated in a single pin electrode structure source for two separate input frequencies of 50kHz and 13.56MHz in the ambient air. The copper pin electrode radius was 360μm, and it was placed in a Pyrex tube with a radius of 3mm for helium gas supply. Due to the input frequency difference, the generated plasmas showed distinct discharge characteristics for their plasma physical appearances, electrical properties, gas temperatures, and optical properties. Strengths and weaknesses of both plasmas were discussed for further applications.

Controllability of small size atmospheric pressure plasma generated at low frequency in a pin to dielectric plane electrode configuration was studied. It was shown that the plasma characteristics could be controlled by geometrical and operational parameters of the experiment. Under most circumstances, continuous glow discharges were observed, but both the corona and/or the dielectric barrier discharge characteristics were observed depending on the position of the pin electrode. The plasma size and the rotational temperature were also varied by the parameters. The rotational temperature was between 300 and 490K, being low enough to treat thermally sensitive materials.